A typical conventional rotation detecting device that is mounted on each of the automotive vehicle wheels so that it can detect the number of revolutions for each of the four wheels, thereby preventing any difference in the revolutions from occurring between each of the wheels has the following construction. That is, the device includes a rotor for the rotation sensor that may be mounted on the rotational part or element of the bearing unit, and a pulse sensor that responds to pulses that are generated by the rotor for the rotation sensor. The rotor for the rotation sensor that provides the function of the pulse generating rotor includes a reinforcing ring having an L-shape cross section. The reinforcing ring has a cylindrical portion that may be fitted and secured to the circumferential surface of the rotational part or element of the bearing unit and a ring portion bent radially from the end edge of said cylindrical portion. A pulse generator means in the form of a multi-pole magnet is arranged on the outer axial side of the ring portion of the reinforcing ring. The pulse sensor is arranged in proximity of the pulse generator means, and may be located axially outside the pulse generator means so that the pulse sensor can respond to the pulses from the pulse generator means. The construction described above is an example that has been developed and used for practical purposes.
In the above construction of the rotation detecting device, in most cases, the reinforcing ring further includes a seal lip formed on the end thereof for providing the sealing function. This construction will be described below in further detail by referring to the appropriate figure.
A typical example of the conventional construction is shown in FIG. 7, and is now described. As shown in FIG. 7, a reinforcing ring 103 has a cylindrical portion 104 fitted and secured to the circumferential surface of the rotational part or element (which corresponds to the outer race 101 in the example shown in FIG. 7) of the bearing unit. The reinforcing ring 103 has a ring portion 105 bent radially from the end edge of the cylindrical portion 104, and a pulse generator ring 106, that has the function of the pulse generator means in the form of a multi-pole magnet, is fastened to the outer axial side of the ring portion 105. A rotation detecting sensor 108 is arranged in proximity of the pulse generator ring 106, and is located axially outside the pulse generator ring 106.
More specifically, the reinforcing ring 103 is formed to have an L-shape cross section, including the cylindrical portion 104 and the ring portion 105 bent radially from the end edge of the cylindrical portion 104, wherein it further includes a seal lip 107 formed on the end thereof as shown in FIG. 7 so that the seal lip 107 can make sliding contact with the circumferential surface of the inner race 102 of the bearing unit. The seal lip 107 may provide the sealing functions that protect the bearing unit comprised of the outer race 101 and inner race 102 against any possible entry of water or foreign matter from the outside.
It may be seen from FIG. 7 that in the conventional rotation detecting device including the rotor for the rotation sensor or pulse generating rotor, the pulse generator ring 106 is arranged in proximity of the rotation detecting sensor, and is therefore located on the outermost side of the device that is exposed to the atmosphere. Thus, the pulse generator ring 106 is always placed under the unfavorable conditions in which it is directly exposed to any splashing water or foreign matter. If any water enters, it may cause rust to gather and it would have the adverse effect on the sensing ability of the rotation detecting sensor 108 to detect the number of revolutions. In even worse situations, any foreign solids might be deposited on some parts of the pulse generator ring 106 and rotation detecting sensor 108. If any foreign solids were to deposit on and enter between the pulse generator ring 106 and the rotation detecting sensor 108, the pulse generator ring 106 might bite the foreign solids, which would cause physical damage to the pulse generator ring 106. This would appear as a serious problem for the conventional rotation detecting device since it would disable the device from detecting the number of revolutions accurately.